The power rating of a clock is 10 cap w , and the cost of electrical energy is 0 point 1 5 dollars per kilowatt-hour. Rounded to the nearest cent, how much does it cost to run the clock for one whole week?

A week has 7 × 24 = 168 hours. A 10-watt clock uses 10 × 168 = 1,680 watt-hours, or 1.68 kilowatt-hours. At $0.15 per kilowatt-hour, the cost is 1.68 × $0.15 = $0.252, which rounds to $0.25: choice B, 0.25 dollars.

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